The present invention relates to processes for preparing polystyrene having .beta. hydroxy group and polyglycol-grafted polystyrenes thereof. More specifically, the invention relates to processes for preparing polystyrene of the formula (I) having hydroxy group at .beta. position in relation to aromatic ring, ##STR1## wherein R.sup.1 and R.sup.2 are the same or different H or CH.sub.3 ; and process for preparing grafted polystyrene of the formula (II) by grafting polyglycols, such as polyethylene glycol, and polyethylenepropylene glycol, onto polystyrene having .beta. hydroxy group, ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are the same or different H or CH.sub.3.
Polystyrene grafted with polyethylene glycol is used in various organic reactions on account of the properties of high swelling and compatibility in various solvents, such as alcohol, dichloromethane, dimethylformamide, acetonitrile, and water; and amphoterism (W. M. Mckenzie, et al., J. Chem. Soc. Chem. 541-543 (1978); J. G. Heffernan, et al., J. Chem. Soc. Perkin II 514-517 (1981); Y. Kimura et al., J. Org. Chem. 48, 385-386 (1983); M. Tomoi, et al., Reactive Polymers 10, 27-36 (1989)).
Such polystyrenes grafted with polyethylene glycol have been prepared either by directly reacting chloromethylated polystyrene, generally known as Merrifield resin, with polyethylene glycol, as reported in Warshavsky, et al., J. Am. Chem. Soc. 101, 4249 (1970); or by introducing hydroxy group onto polystyrene and addition polymerization of ethylene oxide thereto.
One disadvantage of the direct reaction process resides in that cross-linking by polyethylene glycol occurs and makes it hard to obtain resin of desired properties.
Another disadvantage of the direct reaction process is that polystyrene is linked to polyethylene glycol through benzyl-ether linkages, which are unstable and cleaved to produce free polyethylene glycol in the presence of strong acid, such as trifluoroacetic acid, trifluoromethanesulfonic acid, and hydrofluoric acid, that are usually adopted in peptide synthesis, as reported in Y. Kiso, et al., J. Chem., Soc. Chem. Comm. 971 (1979).
In the other processes, conventionally Merrifield resin has been adopted to introduce hydroxy group onto polystyrene, in which hydroxy group is obtained as benzyl alcohol type by reacting Merrifield resin with dimethyl sulfide, as in J. Am. Chem. Soc. 86, 3884 (1964).
German Patent DE 3500180 AI (1986) to Bayer, et al., shows another process using direct reaction of Merrifield resin with tetraethylene glycols which are previously treated by bases, such as KOH, and NaOH.
But the processes using Merrifield resin to introduce hydroxy group have three drawbacks.
One drawback is that the process consists of two steps comprising Merrifield resin synthesis from polystyrene, and hydroxy group introduction.
Another drawback is that chloromethylether, a reactant in synthesizing Merrifield resin, is a known carcinogen.
The other drawback is that the resulting polystyrenes have hydroxy group at the .alpha. position in relation to aromatic ring, which result in benzyl-ether linkages between polystyrene and polyethylene glycol upon grafting.
A preferable process to overcome the above-mentioned drawbacks is to prepare polystyrene having hydroxy group at .beta. position.
M. J. Farrall, et al., in J. Org. Chem. 41, 3877 (1976) discloses a process for introducing .beta. hydroxy group, though the process consists of at least three steps.
Therefore, what is needed to avoid the drawbacks in the prior art is to efficiently introduce hydroxy group onto polystyrene without using a carcinogen, and to graft polyethylene glycol onto polystyrene through a bond which is stable to strong acid medium.
It is thus an object of the present invention to provide an efficient and safe route for preparing polystyrene having a hydroxy group.
It is another object of the present invention to provide polystyrene having hydroxy group at the .beta. position in relation to the aromatic ring.
It is a further object of the present invention to provide polystyrene grafted with polyethylene glycol, or polyethylenepropylene glycol through bonds stable in strongly acidic environment.